U.S. patent application number 13/573696 was filed with the patent office on 2014-04-10 for charged practicles beam apparatus and charged particles beam apparatus design method.
The applicant listed for this patent is Mamoru Nakasuji. Invention is credited to Mamoru Nakasuji.
Application Number | 20140097352 13/573696 |
Document ID | / |
Family ID | 50432008 |
Filed Date | 2014-04-10 |
United States Patent
Application |
20140097352 |
Kind Code |
A1 |
Nakasuji; Mamoru |
April 10, 2014 |
Charged practicles beam apparatus and charged particles beam
apparatus design method
Abstract
Problems to be solved: To obtain higher brightness than Langmuir
limit. Adjust brightness to the optimum value. Method of
resolution: To obtain such beams, the following means and methods
are effective. A charged particles beam apparatus consisting of a
charged particle source, a beam drawing electrode, and a beam
control electrode, wherein; after the charged particles beam source
a condenser lens is designed, and brightness of the charged
particles beam is adjusted by adjusting a magnification factor of
said condenser lens.
Inventors: |
Nakasuji; Mamoru;
(Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nakasuji; Mamoru |
Yokohama-shi |
|
JP |
|
|
Family ID: |
50432008 |
Appl. No.: |
13/573696 |
Filed: |
October 4, 2012 |
Current U.S.
Class: |
250/396R |
Current CPC
Class: |
H01J 3/029 20130101;
H01J 37/26 20130101; H01J 37/06 20130101; H01J 2237/06375 20130101;
H01J 2237/0656 20130101; H01J 2237/06308 20130101; G21K 5/00
20130101 |
Class at
Publication: |
250/396.R |
International
Class: |
G21K 5/00 20060101
G21K005/00 |
Claims
1. A charged particles beam apparatus consisting of a charged
particle beam source, a beam drawing electrode, and a beam control
electrode, wherein; after the charged particles beam source a
condenser lens is designed, and brightness of the charged particles
beam is adjusted by adjusting a magnification factor of said
condenser lens.
2. The charged particles beam apparatus of claim 1, wherein, said
magnification factor of said condenser lens is infinite.
3. The charged particles beam apparatus of claim 1, wherein, said
brightness is adjusted by a distance between the lens principal
plane and the image of the condenser lens.
4. The charged particles beam apparatus of claim 1, wherein, a
distance between the beam source and the lens principal plane of
said condenser lens is larger than 41 mm.
5. The charged particles beam apparatus of claim 1, wherein,
further comprising a second condenser lens, and the distance
between the crossover and the second condenser lens is smaller than
40 mm.
6. A charged particles beam apparatus consisting of a charged
particle source, a beam drawing electrode, a beam control
electrode, and a condenser lens wherein; after the charged
particles beam source the condenser lens is designed, and an
emittance of the charged particles beam is adjusted by adjusting a
magnification factor of the condenser lens.
7. A charged particles beam apparatus design method comprising
steps, after the charged particles beam source a condenser lens is
deposited, the optimum brightness is estimated, and the brightness
is adjusted to said optimum brightness by adjusting a magnification
factor of said condenser lens.
8. The charged particles beam apparatus design method in claim 7,
said optimum brightness is estimated by aberrations of the lens
system, a space charge effect or diffraction and required beam
characteristics.
9. The charged particles beam apparatus design method in claim 7,
said required beam characteristics is a beam size.
10. The charged particles beam apparatus design method in claim 7,
said beam characteristics is a beam diversion angle.
11. The charged particles beam apparatus design method in claim 7,
further comprising a step the brightness as a function of the
distance between the lens principal plane and the image of the
condenser lens is simulated.
12. The charged particles beam apparatus design method in claim 7,
further comprising a step, the second and 3.sup.rd lens is
designed, and the distance between the crossover and the second or
the 3.sup.rd lens is smaller than 40 mm.
13. The charged particles beam apparatus of claim 6, wherein, said
magnification factor of the condenser lens is smaller than 1.
14. The charged particles beam apparatus of claim 1, wherein,
further comprising a second and third condenser lenses, a first
parallel beam is formed by said first lens, and the second parallel
beam is formed by said third condenser lens, and wherein the second
parallel beam size is smaller than the first parallel beam.
15. The charged particles beam apparatus of claim 1, wherein, said
optimum brightness is estimated from the emittance.
16. The charged particles beam apparatus design method in claim 7,
said optimum brightness is estimated from an experience.
17. The charged particles beam apparatus of claim 1, wherein, an
aperture is deposited back of the anode and removes the peripheral
beam.
18. The charged particles beam apparatus of claim 1, wherein, said
magnification factor is larger than 1.
19. The charged particles beam apparatus of claim 1, wherein said
charged particles beam is an ion beam.
20. The charged particles beam apparatus of claim 1, wherein said
charged particles beam source have a spherical electrode and a
spherical mesh electrode.
Description
FIELD OF INVENTION
[0001] This invention pertains to a charged particles beam
apparatus which gives very high brightness characteristics. This
invention also pertains to a charged particles beam apparatus with
a charged particles source. The apparatus include a defect
detection apparatus which detect defects on a semiconductor wafers
by irradiating an charged particles beam to a finely patterned
wafer, detecting SE signal from the patterns, and forming image
data.
BACKGROUND OF INVENTION
[0002] The semiconductor manufacturing process is the era of 45 nm
design rule. The production form is shifting from the small item
mass production represented by DRAM to the multi item small
production like SOC (Silicon on chip). According to this, the
number of manufacturing process is increasing, improvement in yield
in every process is essential, and an inspection of a defect which
is generated in the process become very important.
[0003] According to the higher integration of a semiconductor
device and the finer patterning, an inspection system of high
resolution and high throughput is required. In order to check a
defect on a wafer substrate of 45 nm design rule, it is necessary
to inspect a pattern defect in the pattern having the line width of
40 nm and less, and further to inspect a defect of a particle.
Further, it is necessary to check the electrical defect thereof.
According to an increase in the manufacturing process accompanying
the higher integration of a device, the amount of inspection is
increased. A higher throughput is accordingly required. Further,
tendency toward multilayer of a device is accelerated, an
inspection system is required to have a function of detecting a
contact failure (electrical defect) of a via connecting wire
between layers.
[0004] Further, the electron gun for an ERL radiation optical
source is required a very high brightness and large beam current.
(Nishitani et al, Extended Abstracts (The 53rd Spring Meeting,
2006); The Japanese Society of Applied Physics No. 2, p 798). A
heavy ion source for a heavy ion radiotherapy is also required a
very small Emittance beam.
[0005] Seventy four years ago, Langmuir showed that the current
density in a focused beam of cathode rays was shown to have an
upper limit defined by
J=J.sub.c(e.phi./kT.sub.c+1)sin.sup.2 .alpha., (1)
where J was the maximum current density obtainable in the focused
spot, J.sub.c was the current density at the cathode, .phi. was the
voltage at the focus relative to the cathode, e was the electronic
charge, k was Boltzmann's constant, .alpha. was the half angle
subtended by the cone of electrons which converged on the focused
spot and T.sub.c was the absolute temperature of the cathode. The
necessary initial assumptions were (1) that electrons leaved the
cathode with a Maxwellian distribution of velocities, and (2) that
the focusing system was free from aberration and obeyed the law of
sines.
[0006] By using Liouville's theorem instead of the assumption (2),
J. R. Pierce defined the same results as the eq. (1). As a result
it is seen to be independent of the nature of the concentrating
system when only steady fields are involved.
[0007] From the equation (1) to obtain the high brightness, the
large cathode current density is absolutely necessary, and then a
field emission gun and a Schottky cathode electron gun are much
used as the high brightness electron gun than the thermal cathode
electron gun. As thus the limit has been played a very important
part in developments for the high brightness electron gun.
SUMMARY OF THE INVENTION
[0008] It is a purpose of this invention to obtain the charged
particles apparatus with high brightness beams. To obtain such
beams, the following means and methods are claimed. [0009] 1. A
charged particles beam apparatus consisting of a charged particle
source, a beam drawing electrode, and a beam control electrode,
wherein;
[0010] after the charged particles beam source a condenser lens is
designed, and brightness of the charged particles beam is adjusted
by adjusting a magnification factor of said condenser lens.
[0011] By this charged particles beam, the optimum brightness can
be used. [0012] 2. In the former charged particles beam apparatus,
wherein, said magnification factor of said condenser lens is
infinite. By this charged particles beam apparatus, the maximum
brightness can be used. [0013] 3. The charged particles beam
apparatus in the means 1, wherein, said magnification factor is
adjusted by the image position of the condenser lens.
[0014] By this charged particles beam apparatus, the brightness can
be adjusted to the optimum value without changing the lens position
of the first stage lens. [0015] 4. The charged particles beam
apparatus of the means 1, wherein, The lens position is larger than
41 mm.
[0016] From this means the brightness depend on the lens
magnification factor. [0017] 5. The charged particles beam
apparatus of the means 1, wherein, further comprising a second
condenser lens, and the lens position of the second condenser lens
is smaller than 40 mm.
[0018] From this means the brightness which is formed by the first
stage lens is not depend on the second stage lens. [0019] 6. A
charged particles beam apparatus consisting of a charged particle
source, a beam drawing electrode, a beam control electrode, and a
condenser lens wherein; after the charged particles beam source a
condenser lens is designed, and an Emittance of the charged
particles beam is adjusted by adjusting a magnification factor of
the condenser lens.
[0020] By this means the Emittance can be adjusted. Especially when
the magnification of the condenser lens is smaller than 1, a large
Emittance can be obtained. [0021] 7. A charged particles beam
apparatus design method comprising steps, after the charged
particles beam source a condenser lens is deposited the optimum
brightness is estimated,
[0022] The brightness is adjusted to said optimum brightness, by
adjusting a magnification factor of said condenser lens.
[0023] The optimum brightness can be used by this design method.
[0024] 8. The charged particles beam apparatus design method in the
former method, said optimum brightness is estimated by aberrations
of the lens system, a space charge effect or diffraction and
required beam characteristics.
[0025] On one side the aberrations are increasing function of NA,
on the other hand the space charge effect and the diffraction blur
is decreasing function of NA, and therefore there is optimum NA. As
a result there is the optimum brightness. [0026] 9. The charged
particles beam apparatus design method in the method 7, a said beam
characteristic is a beam size.
[0027] A large beam current with an optimum beam size can be
obtained. [0028] 10. The charged particles beam apparatus design
method in the means 7, a said beam characteristic is a beam
diversion angle.
[0029] A very small diameter beam with a very small beam diversion
angle can be obtained. [0030] 11. The charged particles beam
apparatus design method in the means 7, further comprising a step
The brightness as a function of the image position of the condenser
lens is simulated.
[0031] By this method, the relation between the brightness and the
image position become clear.
[0032] From this means, the distance between the first lens and the
second lens can be designed [0033] 12. The charged particles beam
apparatus design method in claim 7, further comprising a step, the
second and 3.sup.rd lens are designed, and the lens position of the
second or the 3.sup.rd lens is smaller than 40 mm.
[0034] By this method, the high brightness formed by the first
stage lens is kept at the target. [0035] 13. The charged particles
beam apparatus of claim 6, wherein, said magnification factor of
the condenser lens is smaller than 1. A large Emittance beam can be
obtained by this means. [0036] 14. The charged particles beam
apparatus of claim 1, wherein, further comprising a second and
third condenser lenses, a first parallel beam is formed by said
first lens, and the second parallel beam is formed by said third
condenser lens, and wherein the second parallel beam size is
smaller than the first parallel beam.
[0037] A very small Emittance beam can be obtained by this means.
[0038] 15. The charged particles beam apparatus of claim 1,
wherein, said optimum brightness is estimated from the
Emittance.
[0039] In the case where the relations between the brightness and
the Emittance are known and the optimum Emittance is known, the
optimum brightness can be obtain easily. [0040] 16. The charged
particles beam apparatus design method in the means 7, said optimum
brightness is estimated from an experience.
[0041] The case where the optimum brightness is known, the optimum
design can be done easily. [0042] 17. The charged particles beam
apparatus of claim 1, further comprising, an aperture is deposited
back of the anode and removes the peripheral beam. By this means a
very small energy width beam with high brightness can be obtained.
[0043] 18. The charged particles beam apparatus of claim 1, wherein
said magnification factor is larger than 1.
[0044] By this invention, the higher brightness than Langmuir limit
can be obtained. [0045] 19. The charged particles beam apparatus of
means 1, wherein said charged particles beam is a heavy ion.
[0046] The heavy ion beam with very small diverging angle and very
fine diameter can be obtained by this means. [0047] 20. The charged
particles beam apparatus of means 1, wherein said charged particles
beam source have a spherical electrode and a spherical mesh
electrode.
[0048] By this means the charged particles beam, whose current
density at the ion source is small and the current density at the
crossover, is very large can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] FIG. 1 Experimental brightness as a function of the emission
current, here Langmuir limit which are calculated using simulated
axial cathode current density are added in the same type line's
curves without mark. Each maximum separation ratio between the
measured brightness and the simulated Langmuir limit for the same
emission current is shown with an arrow.
[0050] FIG. 2 Electron gun model for this experiment. The cathode
is 90 degree cone shape and its apex is 30 .mu.m radius sphere
shape, a wehnelt electrode is concave cone shape with 2 mm diameter
hole and a cone semi-angle is 70 degrees, and the cathode to an
anode distance is 12 mm.
[0051] FIG. 3 Simulated brightness: B, Emittance: E, and Langmuir
limit as a function the image position. Rectangular marks are the
brightness for the cathode apex radius of curvature of the 120
.mu.m and the lens position: a of 40 mm or less.
[0052] FIG. 4. Electron optics for the brightness measurement. The
broken lines are the parallel beam, and the solid lines are Koehler
illumination conditions. On the target there are Faraday cage with
a Pico ammeter and a gold plated Si edge.
[0053] FIG. 5. Emission current as a function of the wehnelt
voltage, where the solid curve with marks is the measured emission
current, the broken and dotted curves are the simulated emission
current for the wehnelt position of the -0.2 and -0.1 mm,
respectively.
[0054] FIG. 6. Simulated emission current for defining the cathode
temperature. The emission current of the 164 .mu.A give the cathode
temperature of 1419.3 K.
[0055] FIG. 7. The measured and simulated brightness and Langmuir
limit are shown by the solid, broken and dotted curves,
respectively, where the beam energy is the 10 keV and the wehnelt
bias is the -670 V.
[0056] FIG. 8. Measured brightness and simulated Langmuir limit for
Koehler illumination, the beam energy of the 5 keV, and the cathode
temperature of the 1805 K. The simulated brightness is also shown
in the broken with a dot curve.
[0057] FIG. 9. Measured brightness and simulated Langmuir limit for
Koehler illumination and the cathode temperature of the 1805 K,
where the beam energy is the 2 keV. The simulated brightness is
also shown in the dotted curve.
[0058] FIG. 10 The measured and simulated brightness, and Langmuir
limit as a function of the image position: b. The simulated
Emittance is also plotted in the dotted line. The simulated cathode
temperature is the 1419.3 K and the image position: b of 10 meters
is the parallel beam condition
[0059] FIG. 11 Chart for defining the optimum brightness
[0060] FIG. 12 Summary of the brightness measurements, the
abscissa: b/a is the magnification factor of the first stage
lens.
[0061] FIG. 13. Electron optics for forming a fine beam size with
very small diverging angle.
[0062] FIG. 14. An ion source of a small Emittance heavy ion.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0063] Inventor showed an experimental brightness exceeded
simulated Langmuir limit. FIG. 1 shows the experimental brightness
as a function of the emission current, here Langmuir limit which
are calculated using the simulated cathode current density are
added in the same type line's curves. The cathode is 90 degree cone
shape and its apex is a sphere shape, the cathode material, a
crystal orientation, its work function, its beam energy and its
temperature are LaB.sub.6, (100), 2.65 eV, 20 keV and 1900 K,
respectively, and a wehnelt electrode is a flat shape with 1.6 mm
diameter hole. Broken: 11, dotted: 12, broken with a dot: 13,
broken with double dots: 14 and solid: 15 curves are the brightness
for the cathode apex radius of curvatures for the 20, 60, 120, 240,
and 480 .mu.m, respectively. The curves with marks are the
experimental brightness and the ones without mark are the simulated
Langmuir limit. The maximum separations between the experimental
brightness and Langmuir limit for the same emission current are
calculated, and added in this figure with arrows. The each
experimental brightness for the cathode apex radius of curvature of
the 20, 60, 120, 240, and 480 .mu.m is 8.7, 5.3, 3.3, 2.4 and 3.9
times higher brightness than each Langmuir limit, respectively. For
the entire cathode and the emission current, the measured
brightness is higher than Langmuir limit These experimental data
are too old to be believed against the theory of Langmuir limit,
and then some simulations and the brightness measurements are
done.
[0064] A brightness calculation model is formed as the electron
guns with the LaB.sub.6 cathodes and a magnetic lens, for the
comparison between the simulation and the old measured brightness,
where the cathode apex radius of curvature: Rcc are the 20, 60,
120, 240, and 480 .mu.m.
[0065] FIG. 2 is an example of the electron gun with the 60 .mu.m
apex radius of curvature cathode. Where 21 is a wehnelt electrode,
22 is an anode and 23 is a cathode, respectively. The magnetic lens
is a popular lens with a lens gap of 2 mm and a bore radius of 5
mm, and the magnetic field is formed in the z-coordinate from -90
mm to 50 mm. The cathode temperature is the 1900 K and the beam
energy is the 20 keV. The lens position or a distance between the
beam source and the lens principal plane: a, the image position or
the distance between the lens principal plane and the image: b, the
beam energy, and a magnetic lens field are given to a commercially
available software: ABER-5, and the lens excitation satisfying the
image position: b is calculated, where the lens position: a is the
180 mm from the cathode. By using these lens excitations and the
electron gun data shown in Table-1, the brightness are calculated.
In this model mesh sizes around a cathode surface are particularly
finer than the other area from the cathode to the target. Distances
from the cathode to an anode, from the cathode to the wehnelt, and
from the cathode to the target are 7.5, 0.2 and 25 mm,
respectively. The simulation is done by use of a commercially
available computer program: SOURCE-version 1.5. Emittance are also
calculated, as a product of a .phi..sub.co and a .theta..sub.90,
where the .phi..sub.co is the crossover diameter and the
.theta..sub.90 is defined as an emission angle that the brightness
is 90% of the axial brightness.
[0066] FIG. 3 is the simulated axial brightness as a function of
the image position: b. Where 31 is Langmuir limit and 32 is a
simulated brightness for the cathode curvature of 120 .mu.m Rcc and
the lens position of 40 mm. The lens excitations giving each image
position: b is shown in a top of the figure. For each emission
current which gives the maximum separation, between the
experimental brightness and simulated Langmuir limit, the
simulation is done. For each the cathode apex radius of curvature:
Rcc of the 20, 60, 120, 240 and 480 .mu.m, the emission current is
251, 813, 490, 514, and 999 .mu.A, respectively, as seen from the
arrow's coordinate in FIG. 1. Each brightness and Langmuir limit is
calculated for the cathode apex radius of curvature and the
emission current. Increasing curves, decreasing curves and flat
lines for the image position: b of from 10 to 1000 mm, are the
brightness, Emittance and Langmuir limit, respectively. The
simulated results for the Rcc of the 20, 60, 120, 240, and 480
.mu.m are shown by the broken, dotted, broken with a dot, broken
with double dots, and solid line curves, respectively. Rectangle
marks are the simulated brightness for the Rcc of the 120 .mu.m
cathode and the lens position: a of 40 mm or less.
[0067] As seen in FIG. 3, the simulated brightness change
drastically, when the lens excitation is valid. This result is
inconsistent with the familiar law for ordinary optical instruments
that the brightness of source of light cannot be changed by any
focusing process.
[0068] The simulated brightness is nearly proportional to a square
of the image position: b, for at least from 40 mm to the 1000 mm of
b. When the cathode apex radius of curvature are the 120, 240 and
480 .mu.m, the brightness are nearly equal to Langmuir limit at the
image position b are 180 mm, which is equal to the lens position:
a. When the cathode apex radius of curvature are the 20 and 60
.mu.m, the brightness are equal to Langmuir limit at the image
position b of 68 and 120 mm, which are smaller than the lens
position of the 180 mm.
[0069] Emittance are also calculated and shown for the cathode apex
radius of curvature of the 20 and 480 .mu.m Rcc which give the
maximum and minimum axial cathode current density, respectively.
The Emittance is a decreasing function of the image position b,
when the brightness is the increasing function of the b, and it is
the increasing function of the b, when the brightness is the
decreasing function of the b. The each Emittance has the maximum
and minimum values at the image position where the brightness has
the minimum and maximum values, respectively.
[0070] For example, the brightness is lower than a 1.times.10.sup.7
A/cm.sup.2 sr, the Emittance is higher than 13 .mu.mmrad for the 20
.mu.m Rcc cathode and higher than 17 .mu.mmrad for the 480 .mu.m
Rcc cathode. From this simulation it may be necessary that an
acceptance of the measurement system is lower than the 13 .mu.mmrad
for the brightness measurement lower than the 1.times.10.sup.7
A/cm.sup.2 sr.
[0071] When the lens position: a is smaller than 40 mm and the
cathode apex radius of curvature is the 120 .mu.m, the simulated
brightness is independent on the image position: b and nearly equal
to the simulated Langmuir limit, as shown by the square marks in
FIG. 3. When the cathode is the Schottky emission cathode, similar
results are obtained, however, the lens position: a in which the
simulated brightness does not depend on the image position is
smaller than 49 mm or less.
[0072] The brightness measurements are done using an electron beam
lithography system: EBW-7500C made in ELIONIX INC. The measurements
are done for the electron gun with the (100) orientation LaB.sub.6
cathode. The lithography system has been designed for the Schottky
cathode electron gun, and have three problems for the LaB.sub.6
electron gun, (1) that the maximum heating power for the cathode is
1.9 Ampere at first and too small for the LaB.sub.6 cathode, (2)
that the maximum emission current is limited below 190 .mu.A, and
(3) that the excitation of the second lens is programmed so that
the image position of the second lens: c is 18 mm for a lens
position of 60 mm, and then the minimum focus length is 13.85 mm.
The heating power problem is resolved during the experiment.
[0073] FIG. 4 is an electron optics for the EBW-7500C. Where 41 is
the cathode, 42 is the lens position of the first lens: 44, 43 is a
lens alignment deflector, 45 is the image position for the first
lens, 46 is a blanking aperture, 47 is the second condenser lens,
48 is the image position of the second lens, 49 is the objective
lens, 410 is a target and 411 is a gold plated Si edge. The
experiment is done for two lens conditions, those are (1) that the
electron beam diverged from the electron gun is focused by the
first lens and become the parallel beam and the crossover image is
reduced by a second lens and by an objective lens, as shown by the
broken lines in FIG. 4, and (2) Koehler illumination system that
the diverged beam from the electron gun is converged by the first
lens and focused at a designed position before the second lens and
the crossover image is magnified by the second lens and focuses on
a NA aperture. A shaped beam formed by a blanking aperture is
reduced by the second and the objective lenses and focused on the
target. This optical figure is shown by the solid lines in FIG. 5.
The lens position: a is 123 mm, and the minimum image position of
the second lens: c is the 13.85 mm. The blanking aperture and the
NA aperture diameters are changeable to 30,60, or 500 .mu.m, and
40, 80 or 160 .mu.m, respectively.
[0074] For the lens condition of (1), three measurements are done
for the same emission current condition with three beam semi-angle:
.alpha. conditions to increase reliability for the measured
brightness, where the NA aperture diameter: dNA and the image
position of the second lens: c are varied. The beam energy is 10
keV and the beam current is measured by a Faraday cage on the
target. The beam diameter .phi..sub.b is defined to be the distance
between the readings corresponding to 10% and 90% of the SE
integrated intensity distribution during the scanning at the edge
of the gold plating silicon edge. The measured beam current, the
measured beam diameter and the measured brightness with these set
up conditions are listed in Table-II. The beam semi angle .alpha.
and the brightness B are calculated as in the eq. (2) and (3),
respectively,
.alpha.=d.sub.NA(d+e-c)/2f(d-c) (2)
B=4I.sub.b/(.pi..phi..sub.b.alpha.).sup.2, (3)
where the d, e, and f are 157, 167 and 37 mm, respectively.
TABLE-US-00001 TABLE II Set up conditions and the measured
brightness: B dNA c .alpha. I.sub.b .phi..sub.b B Acceptance No.
(.mu.m) (mm) (mrad) (nA) (nm) (A/cm.sup.2sr) (.mu. mmrad) 1 40
13.85 1.17 0.44 243 2.21 .times. 0.sup.5 0.284 2 80 13.85 2.34 1.64
252 1.91 .times. 0.sup.5 0.589 3 40 40 1.31 1.08 313 2.6 .times.
10.sup.5 0.41
[0075] For these three measurements, the emission current is 164
.mu.A and the cathode temperature which was measured previously is
1186 K. However, for the temperature and the work function of the
2.65 eV the simulated maximum emission current is only 2.19 .mu.A,
therefore the more reliable cathode temperature is studied. FIG. 6
is the measured emission current: 61 as a function of the wehnelt
voltage: V.sub.w where the cathode temperature is 1805 K, and the
electron gun is operated in a space charge limited condition. The
emission current is restricted not by the cathode temperature but
by a source capacity for the emission current.
[0076] Firstly, the wehnelt position is defined. The broken: 52 and
dotted: 53 lines are the simulated emission current for the wehnelt
position of -0.1 and -0.2 mm, respectively; here the z-coordinate
of the cathode apex is the 0. As seen in this figure, the broken
curve is proximity to the measured emission characteristics, and
then wehnelt position is defined as the -0.2 mm. Secondly, the
cathode temperature is defined. FIG. 6 is the simulated emission
current: 61 as a function of the cathode temperature for the model
in FIG. 4, when the wehnelt position of the -0.2 mm and the wehnelt
voltage of -500 V. When the wehnelt voltage is the -500 volt, the
measured emission current is the 164 .mu.A, and then the cathode
temperature is defined as 1419.3 K.
[0077] For such a low cathode temperature, the crossover and an
emission direction are separated as five beams and four directions,
respectively, however only a central part of the beam pass through
the NA aperture, because the wehnelt voltage is so shallow that the
emission from the (310) and (301) orientation diverge so large
angle that they do not pass through the NA aperture, fortunately.
Therefore a very fine and intense beam is measured. As shown in the
last column in Table-II, each acceptance is calculated as the
product of the beam half angle: .alpha. and the measured beam
diameter: .phi..sub.b. If the Emittance of the electron gun is
larger than the acceptance, the brightness calculated by the eq.
(3) has no problem. However, if the Emittance is smaller than the
acceptance, the NA aperture is only partially illuminated and the
measured brightness is not the axial brightness but an average
brightness.
[0078] The heating current is improved from the 1.9 Ampere to 2.4
Ampere, and the cathode temperature previously measured is 1604 K.
The beam energy is the 10 keV and the lens condition is the same as
before. For the wehnelt voltage of -670 V, the emission current
varies 37, 57, and 96 .mu.A, therefore the cathode temperature is
not a stationary temperature but a transition state. The cathode
temperature increases very slowly, and each the beam diameter and
the beam current for these emission currents can be measured within
a small cathode temperature change.
[0079] The measured pairs of the beam current: I.sub.b and the beam
diameter: .phi..sub.b for the emission current of the 37, 57, and
96 .mu.A are 0.26 nA and 666.3 nm; 0.5 nA and 675 nm; and 1 nA and
769.8 nm, respectively. The NA aperture diameter and the image
position of the second lens are the 40 .mu.m and the 13.85 mm,
respectively and then the beam semi-angle: .alpha. is 1.17 mrad.
The brightness is calculated as 1.7.times.10.sup.4,
3.19.times.10.sup.4, and 4.91.times.10.sup.4A/cm.sup.2 sr, for the
emission current of the 37, 57, and 96 .mu.A, respectively. For
this measurement a SEM image of the Au plated Si edge is not a
single line but double lines, and the SE integrated intensity
distribution for the beam diameter measurement is not an error
function but two stepped waveform, unfortunately. Therefore the
crossover image is separated roughly perpendicular direction to the
edge, and then the beam diameter is measured as larger than the
single spot and the NA aperture is only partially illuminated.
Because of these two problems three brightness are measured as much
lower values than the axial brightness.
[0080] The brightness as a function of the emission current is
shown in FIG. 8. Each Langmuir limit: 82 is calculated from the
simulated axial cathode current density for each emission current
and the cathode temperature of the 1400, 1426, and 1459 K. The
measured brightness for the temperature of the 1459 K is 21.9 times
higher than Langmuir limit. Where 81 is the simulated brightness
.times.0.01.
[0081] The following measurements are done for the condition (2)
that is, the Koehler illumination condition. The heating current is
improved from the 2.4 Ampere to 2.6 Ampere, the previously measured
cathode temperature is the 1805 K and the emission direction and
the crossover for the emission current smaller than the 190 .mu.A
become an axial symmetric and a single Gaussian crossover,
respectively. For the beam energy of 5 keV, the brightness
measurement is done. The measured beam diameter is 1000 nm. On the
one side the reduced aperture image diameter of the blanking
aperture is 1088 nm, and a calculated distance between the readings
corresponding to the 10% and 90% of the 1088 nm is 758 nm, for a
square intensity distribution beam. The difference between the 1000
and the 758 nm are caused by an axial chromatic aberration, a space
charge blur and a measuring error. Here the 1000 nm is adopted for
the brightness defines.
[0082] FIG. 9 shows the brightness as a function of the emission
current, and Langmuir limit: 92 which are calculated by the
simulated axial cathode current density and the cathode temperature
of the 1805 K. For the measurement-1: 93 and -2: 94, the electron
gun alignment is done so that an absorbed current by the NA
aperture and by the Faraday cage are maximized, respectively. It is
seen that the electron gun alignment method give little effect to
the brightness measurement. As shown in FIG. 9, five point values
are higher than Langmuir limit and six point values are lower than
Langmuir limit. Therefore, the measured brightness is comparable to
the simulated Langmuir limit. Where 91 is the simulated
brightness.
[0083] FIG. 10 is the simulated: 101, measured brightness: 102 and
Langmuir limit: 103 as a function of the emission current, where
the beam energy is 2 keV, the optics is Koehler illumination and
the beam size is selected as the 758 nm. As seen in FIG. 10, the
measured brightness is comparable to Langmuir limit These measured
brightness in FIGS. 9 and 10 are adopted as the 1000 nm and the 758
nm, respectively for the beam diameter.
[0084] (1) Measurement for the Parallel Beam Condition
[0085] Using the cathode temperature of the 1419.3 K, the model in
FIG. 4 and the magnetic lens which is designed at the 123 mm from
the cathode, the brightness are simulated. The magnetic lens is a
typical lens with the lens gap of 3 mm and the bore radius of 11 mm
and the magnetic field is formed for the z-coordinate from -100 mm
to 80 mm. Emittance is also calculated as the product of the
.phi..sub.co and the .phi..sub.90. The cathode current density is
also simulated as 0.103 A/cm.sup.2. Using this cathode current
density Langmuir limit is calculated as 2.68.times.10.sup.3
A/cm.sup.2 sr. These simulated results and measured brightness in
Table-II and simulated Langmuir limit as a function of the image
position: b are shown in FIG. 7. The measured three brightness
values: 72 are about 10 times lower than the simulated brightness;
71; however they are from 73 to 100 times higher than simulated
Langmuir limit: 74. In FIG. 7, when the image position: b is 10000
mm, the simulated Emittance: 73 is 0.36 .mu.mmrad and larger than
the acceptance of No. 1: 0.287, and smaller than the 0.582 and 0.41
mmrad, which are the acceptances of No. 2 and No. 3, respectively.
Therefore, the measured brightness No. 1 is no problem, however the
brightness No. 2 and No. 3 are lower value than the axial
brightness. It can be said that the maximum measured brightness is
at least 100 times higher than Langmuir limit
[0086] In FIG. 8 the measured and simulated brightness for the
heating current of the 2.4 Ampere are compared, where the simulated
brightness: 81 is multiplied by 0.01. The simulated brightness: is
23.9 times higher than the measured one. This high separation ratio
is the course of the crossover separation. In spite of the
crossover separation problem, the measured brightness is 23 times
higher than Langmuir limit: 82.
[0087] (2) Measurement for the Cathode Temperature of the 1805 K
and Koehler Illumination Condition
[0088] For the lens position: a of the 123 mm from the cathode, the
image position b of 108 mm, the beam energy of the 5 keV and the
cathode temperature of the 1805 K, the brightness: 93 and 94 and
the cathode current density as a function of the emission current
are simulated and added in FIG. 9. When the image position is a
little smaller than the lens position, the measured brightness is
comparable to the Langmuir limit: 92 and about 28% of the simulated
brightness: 91.
[0089] For the beam energy of the 2 keV and the image position: b
of the 108 mm the brightness and the axial cathode current density
as a function of the emission current is simulated. From the beam
energy of the 2 keV, the cathode temperature, and the simulated
axial cathode current density, Langmuir limit is calculated and
added in FIG. 10. When the image position is a little smaller than
the lens position, the measured brightness is comparable to the
Langmuir limit: 103 and about 20% of the simulated brightness: 101.
As the beam diameter of the 758 nm instead of 1000 nm is adopted,
the measured brightness are comparable to Langmuir limit and about
35% of the simulated brightness: 101.
[0090] From the FIGS. 1 and 10 it is said that all the measured
brightness are higher than Langmuir limit and lower than the
simulated brightness and for the electron gun with different
cathode apex radius of curvatures, the greater part of the measured
brightness are nearer to the simulated brightness than Langmuir
limit
[0091] From the simulated brightness and Emittance in FIG. 3 it is
expected that for the brightness measurement smaller than the
1.times.10.sup.7 A/cm.sup.2 sr, the Emittance is larger than 13
.mu.mmrad and sufficiently larger than the acceptance values in
Table-II. However the simulation for the cathode temperature of the
1419.3 K and the image position: b of the 10000 mm, the simulated
Emittance is only the 3.6 u mmrad, and comparable or smaller than
the acceptance of the apparatus. Therefore, the beam half angle
.alpha. must be measured not from the NA aperture size but from a
measured beam diameter on the NA aperture: 0 NA. The beam
half-angle .alpha. become to the eq. (4),
.alpha.=.phi..sub.NA(d+e-c)/(d-c)f. (4)
The beam diameter .phi..sub.NA can be defined to be the distance
between the readings corresponding to the 10% and 90% of a
transmission electron integrated intensity distribution during the
scanning at the edge of the NA aperture.
[0092] The brightness higher than the simulated Langmuir limit is
measured using two measuring system and for the many emission
conditions and for six sized cathodes. If the simulated cathode
current density is near to the real value, the brightness higher
than Langmuir limit is reliable, because there is few factor of
measuring higher brightness than the real value.
[0093] For three lens excitation conditions, these are (1) the
parallel beam condition, (2) the image position: b is larger than
the lens position: a, and (3) the image position: b is a little
smaller than the lens position: a, the ratios between the measured
brightness and the simulated Langmuir limit are from the 73 to the
100, from the 2.4 to the 8.7, and comparable, respectively. These
experimental brightness for three lens excitation conditions are
consistent to the simulation that the brightness depends on the
first lens excitation. From these measurements it may say that the
brightness can be adjusted by changing the first lens
excitation.
[0094] FIG. 11 is a method of defining the optimum brightness
measurement method in this invention. Where 111 is the space charge
effect for the beam current of 100 nA, the axial chromatic
aberration: 116, a coma 118, and a spherical aberration 119 as a
function of NA are added and shown 112 as a total blur. A required
beam size is 20 nm and an effective beam size D.sub.eff is
calculated as eq. 11, and shown a curve 113.
D.sub.eff= (20.sup.2-D.sub.total.sup.2).
[0095] Line 114 is a tangent of the curve 113. From the difference
between the line 111 and 114, 46 nA for the 114 is obtained. From
the equation shown bottom in FIG. 11, the optimum brightness is
obtained as B=1.63.times.10.sup.7 A/cm.sup.2 sr.
[0096] The optimum brightness can be defined from an experience.
FIG. 12 is a summary of the experiment. An abscissa is a ratio
between the image position/lens position: b/a, and an ordinate is
the ratio between the Simulated or the measured brightness/Langmuir
limit. 121, 122 and 113 are for the measured brightness and 122,
124 and 126 are for the simulated brightness. The data: 122 and 124
are the data for the cathode radius of curvature of 20 .mu.m Rcc.
As see in FIG. 12. The simulated and the measured brightness depend
on the image position of the first stage lens. The ratio between
the image position/lens position: b/a is a magnification of the
first stage lens, and therefore this figure shows that the
brightness and Emittance can be controlled by adjusting the
magnification factor of the first stage lens
[0097] FIG. 13 is an example of the charged particles beam source
for an ERL radiation optical source. The charged particles beam:
135 emitted from the charged particles beam source: 131 are
condensed by the first stage lens: 132, formed parallel beam: 136,
and focused by the second lens: 133, and formed a crossover: 138
before the 3rd lens 134. The charged particles beam from the
crossover: 138 is condensed by the 3rd lens: 134 and make the
parallel beam: 137. The lens position of the first lens: 132 must
be larger than 41 mm, and the lens position of the 3rd lens must be
smaller than 40 mm. When the ratio: (the lens position of the first
lens/the lens position of the 3rd lens) is sufficiently larger than
1, the parallel beam 137 is very small diameter. The brightness of
this beam is very high, and then the diverging angle of this beam
is very small. When the image position of the second lens is
smaller than the lens position of the 3rd lens, the beam diameter
of the second parallel beam is smaller than that of the first
parallel beam.
[0098] FIG. 14 is an ion source with a small Emittance.
[0099] Between a spherical electrode: 141 and a spherical mesh
electrode: 142 a high frequency electromagnetic wave is added from
a high frequency generator: 150. When a gas for the heavy ion is
added from a nozzle: 143, a gas discharge is occur, the ion is
generated and an ion beam is drawn by a beam drawing electrode:
145. The ion beam make the crossover at a position around the beam
drawing electrode. The distance between the crossover and an
electro-static lens: 146, 147 and 148 is larger than 41 mm, and the
lens forms the parallel beam, and then a very small Emittance ion
beam is obtained. This ion beam have very small diverging angle.
When the ion beam is introduced to an accelerator, the heavy ion
beam with a large beam current is irradiated to cancer cell.
[0100] Though most of discussions are done regarding the electron
beam, for the charged particles beam above story can be stand.
EFFECT OF THIS INVENTION
[0101] As above explained the best mode of the electron beam
apparatus for this invention, this invention enable to obtain the
charged particles beam apparatus which gives the brightness higher
than Langmuir limit and the charged particles beam with the small
energy width. Therefore, the finely focused multiple beam with
large beam current are formed around an optical axis, and the SEs
from the electron beam far from the optical axis can be detected
easily, the emission current can be small, and then the space
charge effect is small. And when the small aperture is deposited
back of the anode and remove the peripheral beam, the energy width
increase due to the space charge effect become small.
TABLE-US-00002 TABLE-1 Data for Simulation Mesh Title sz.dat 30 umR
1 21 41 51 71 171 221 251 1900 k 1 -1.5 -2.5 -2.1838 -1.9838 2 12
17 20. 56 -.4 -.4 -.0 0.2 2 12 17 20. 61 -.237573 -.233432 -.0 .2 2
12 17 20. Units mm 91 -.008786 .005355 .05 .25 2 12 17 20. 121 0.
.02 .08 .3 2 12 17 20. Cathode 1 21 41 51 71 171 221 251 region 61
121 1 0.3 5. 7.2 7.2 9. 17. 17. 17. 56 .3 1. 1.2 1.2 2. 8.5 2.2 2.2
61 .25 .3 1. 1. 1. 2.2 2. 2. 91 0.021213 .035355 .1 .2 .5 1. 1. 1.
Temperatue 1900 121 0. 0. 0. 0. 0. 0. 0. 0. Work Function 2.65
Richardson constant 70 1 21 41 51 71 171 221 251 1 0. 0. 0. 0. 0.
0. 0. 0. 56 0. 0. 0. 0. 0. 0. 0. 0. Space charge on 61 0. 0. 0. 0.
0. 0. 0. 0. Rays 15 91 0.03 0.05 0. 0. 0. 0. 0. 0. Cycles 30 121 0.
0. 0. 0. 0. 0. 0. 0. Time step factor 0.33 Convergence 0.002 1 21
41 51 71 171 221 251 1 0. 0. 0. 0. 0. 0. 0. 0. 56 0. 0. 0. 0. 0. 0.
0. 0. Magnetic lens cl1 61 0. 0. 0. 0. 0. 0. 0. 0. Position 123 91
0. 0. 0. 0. 0. 0. 0. 0. Excitation 685AT 121 0. 0. 0. 0. 0. 0. 0.
0. Relativity on 41 51 1 61 -870 171 221 1 56 20000. 221 241 1 56
20000.00 Save trajectories on Rotational Symmetry 1 0. 121 0. 1 0.
41 -870 sz.con 51 -870 171 20000.00 251 20000. Tme step factor 0.3
1 20000.00 Rays 249 121 20000.00
* * * * *